It is known that so-called aseptic packages can be produced by packing sterilized contents into sterilized packing containers under controlled aseptic conditions. A known aseptic package of non-returnable character is manufactured with the help of a packing machine which produces packages from a web of laminated packing material. The longitudinal edges of the web are combined with one another so as to form a tube which is filled with the intended, sterilized contents and which is divided into sealed container units through repeated flattening and sealing of the tube along narrow zones located transversely to the tube. After separation by means of cuts in the sealing zones and possible fold-forming and sealing, the container units leave the machine in the form of finished packages of usually parallelepipedic shape.
To ensure that the sterilized contents introduced preserve their sterility in the package, the web, or at least the side of the web which is intended to be facing towards the inside of the tube, must be sterilized before it comes into contact with the contents. The sterilization of the web is usually performed by bringing the web into contact with a chemical sterilizing agent by passing the web through a heated bath containing the sterilizing agent. Thereafter, any excess sterilizing liquid is squeezed out of the web with the help of co-operating pressure rollers between which the web is conducted. Remaining residual amounts of sterilizing liquid are driven off the web with the help of hot air which is blown towards one or both sides of the web. The web is then converted to a tube with the sterilized inside ready to receive the particular sterilized contents.
Through use of hydrogen peroxide, which is an example of a frequently used sterilizing agent on an aseptic packing machine of the type described, it has been found that bacteriological killing effects, which fully comply with prescribed health conditions, are achieved if the sterilizing agent is used in the form of a solution containing approx. 35% hydrogen peroxide (H.sub.2 O.sub.2) at a temperature of approx. 65.degree.-75.degree. C., preferably approx. 70.degree. C. However the contact between the material web and the sterilizing solution must be maintained at least for a certain specified time. Assuming a normal production speed of a conventional packing machine, the aforementioned contact time corresponds to a certain contact distance, which implies that the bath containing the sterilizing solution, must belong enough to provide an accessible pass-through distance for the moving material web that corresponds to contact distance. For practical reasons, such as the lack of space, the bath frequently is arranged in the form of a so-called deep bath, moreover the bath is located in a vertical container arranged before the forming and filling zone of the tube, whose height appreciably exceeds its width. The material web which is to be sterilized is then passed in a vertical loop through the bath and around a roller arranged in the lower part of the container. The roller helps control the moving material web so that at any time each part of the web is below the liquid level and is in contact with the sterilizing solution during a period, calculated from the entry of the web into the bath to the web's exit from it, that corresponds at least to the required contact time. A further advantage gained by using this deep bath is that good contact between the material passing through the bath and the sterilizing solution in the bath is ensured, at least in the lower part of the container where the contact is intensified as a result of the prevailing higher hydrostatic pressure which presses the sterilizing solution towards the passing web.
The intensified contact between the hydrogen peroxide solution and the material web is, of course, an advantages from a point of view of bacteriological killing. However, the intensified contact also increases the risk that the hydrogen peroxide solution will penetrate into and degrade the liquid-absorbent fibrous layer of the material web through cut edges of the web. This risk, which is connected with the hydrostatic pressure in the bath and consequently increases at the same rate as the rate of increase in the hydrostatic static pressure, is aggravated somewhat also by the fact that the material web in the known sterilization system before it enters into the bath has a temperature that corresponds to ambient temperature which in any case is appreciably lower than the temperature of the heated sterilization bath (approx. 65.degree.-75.degree. C.), this means that after entering the bath the relatively colder material web will pass through a certain part of the bath during which the web absorbs heat from the surrounding hydrogen peroxide solution as a result the solution is cooled down before temperature equilibrium between the hydrogen peroxide solution and the web has been reached. As mentioned previously, the bacteriological killing effect is dependent, among other things, on the temperature of the hydrogen peroxide solution. Thus in order to compensate for the less active bacteria-killing contact stretch, through which the material web is liable to pass before the required equilibrium of temperature between the hydrogen peroxide solution and the material web has been able to establish itself, it has been necessary to "overdimension" the bath somewhat. That is to say it has been necessary to design the bath to be deeper than would be the case if this temperature equilibrium had established itself instantaneously upon entry of the web into the bath. The overdimensioning of the bath results in a further increase in hydrostatic pressure as well as an increase in the risk that the liquid will penetrate into the web in the deeper parts of the bath, alternatively, the bath can be made wider but that anternative requires more space.